Process of producing high-percent caoutchouc solutions



llatented May l6, 1933 FFEQE RUDOLF OECKINGHAUS, OF METTMANN, GERMANY,ASSIGNOB T IMMALIN-WERKE OHEMISCl-IE FABRICK EISENDRATH G. M. B. 1-1.,OF METTMANN, GERMANY rnoonss or rnonnorne iiieir-rnncnn'r GAOUTCHOUGsoLU'rIoivs No Drawing. Application filed November 20, 1930, Serial No.497,082, and in Germany August 26, 1930.

A characteristic property of caoutchouc is, that it will swell graduallyin organic solvents such as ether,'benzine, benzene, chlorine,hydrocarbons, carbon disulfide and the like and together with suchsolvents will form thick, hardly movable jellies. This conversion willtake place already at a caoutchouc content of only 2 to 5% and independence of the nature of the caoutchouc and the dissolvingconditions. Such tumefactions will, however, turn more liquid when leftto themselves for some time or heated, especially in the presence oflight. It is also possible to produce thinly liquid caoutchouc solutionsby masticizing or milling the caoutchouc for a relatively long periodbefore the solvent is added in such a manner that the material isovermilled, i. e. the nerves of the same are destroyed. This treatmentis especially effective when carried out at raised temperature. Anothermethod consists in adding softening, high-boiling plasticizing agents tothe caoutchouc during the rolling or milling operation. Suitable agentsfor this purpose are for instance tetrahydro naphthalene and the esterof this compound. It is, however, not possible by means of the methodshitherto known to produce solutions containing more than of caoutchouc.Further this result can only be obtained at high working expenses andthe nerve system of the caoutchouc will be severely damaged through thetreatment.

Now, according to the present invention caoutchouc solutions containing15, and even of caoutchouc may be obtained in an exceedingly simplemanner by adding an oxidizing agent, for instance nitric acid,to thesolution. The caoutchouc solutions obtained by this treatment may beused for dipping, staining and spraying purposes. This effect of theoxidizing agents is very surprising, because strong nitric acid andozone react violently with crude or vulcanized caoutchouc, wherebynitrosites respectively ozonides are formed. "When certain conditionswith regard to the amount, the concentration and the duration of theaction of the oxidizing agent are maintained it is,

however, in accordance with the present inlot is added.

vention possible to conduct the reaction in such a manner that thesolubility of the caoutchouc or the fluidity of the caoutchouc solutionis increased without any essential change in the nature or structure ofthe caoutchouc taking place.

Example 1 10 kg. of Ceylon-crepe or fine hard cure Pararubber are cut upinto pieces of hand size and these pieces are filled into a container ofsuitable size, which is equipped with a cover and'an agitator (or amastifier). Into this container now the fourto sixfold amount of anorganic solvent is poured and the mass is stirred from time to timeuntil a homogeneous, thick massis Example 2 This treatmentdifferentiates from that described under Example 1 in that the nitricacid at once is added to the solvent. The effect of the acid may beneutralized at any desired moment by adding a substance of alkalinereaction.

The exact nature of the reaction between the nitric acid and thecaoutchouc solution is not as yet positively known. Apparently thenitric acid reacts chemically with the solved caoutchouc and eventuallyalso with the solvent, which is usually benzine which is well known as asolvent for caoutchouc or with the natural aromatic ingredient of thebenzine. However this may be, the nitric acid as stated above is usedduring the reaction and therefore causes the more physical effect of thecleavage of the caoutchouc macro molecules. The process dependsessentially upon the right proportion of the nitric acid used and theminimizing of the nitric acid to the point that only such cleavage ofthe caoutchouc macro molecules is obtained as to lower the viscositywithout an appreciable loss of the nerve (of the original condition) ofthe caoutchouo.

It will be evident that such concentrated caoutchouc solutions ofrelatively low viscosity are of great practical importance. Saidsolutions may be employed in natural or filled state, for instance dyedwith covering pigments. The dyed solutions may for instance be used forapplying non-crumbling colored high-glaze coatings to articles of softrubber, such as balls and toys.

The high-percent caoutchouc solutions according to the invention areespecially valuable in the producing of coatings for articles of softrubber which are subjected to severe mechanical strains, such as rubberboots and the like.

Suitably dyed high-percentage caoutchouc solutions may further be usedwith advan tage for producing durable colored coatings of high coveringpower for such rubber articles which must be sold at relatively lowprices and therefore hitherto could not be dyed thoroughly and deliveredin unobjectionable state. Such articles are for instance rubber heels,rubber soles, toys, rubber plates, rubber carpets, rubber mats and thelike. Foot wear is an. article which is subject to the changes of themode or fashion and especially the color of foot wear changes Veryfrequently. From an economical point of View it is therefore notadvisable to dye the mass of the rubber heels in all the colors in whichthe shoes or the like are to be delivered. In this case the heels wouldbecome rather costly and it would be necessary to employ cheap materialof low quality for the other parts of the shoes in order to be able tosell the same with profit at normal prices.

Now, according to the present invention it is possible to produce heels,soles and the like of a single, neutral color (for instance grey orblack) and to coat said bodies with a durable coating of any desiredcolor obtained from the said high-percent caoutchouc solutions.

The high-percent solutions according to the invention may also be usedfor repairing cracks and other defects in soft rubber articles. Hithertosuch defects were remedied by attaching a thin rubber plate to the spotto be repaired by means of a solution poor in caoutchouc. The driedcaoutchouc solution may of course be hardened in the usual manner byvulcanizing it in cold state.

The filled, non-filled, dyed or undyed high-percent caoutchouc solutionsmay also be used for producing articles which are dipped into or coatedwith caoutchouc. The working process is in this case much simpler thanthe processes hitherto used.

I claim:

1. A high percent oaoutchouc solution of low viscosity, comprising asolution of caoutchouc in an organic solvent and nitric acid in theproportion of from one to three percent of the acid with respect to thecaoutchouc.

2. As a new composition of matter, the physical reaction product of asolution of caoutchouc in an organic solvent in the proportion of from15 to 25 per cent of the caoutchouc with respect to the solvent andnitric acid in the proportion of from 1 to 3 percent of the acid withrespect to the caoutchouc.

3. The herein described process of making a high percent caoutclioucsolution of low viscosity and adapted for use in dipping, spreading andspraying, and consisting in adding an organic solvent to a mass ofpieces of rubber in the proportion of from about 15 to 25 per cent orthe caoutchouc with re spect to the solvent, stirring such mixture untila homogeneous thick mass is formed, adding nitric acid to the mixture inthe proportion of from 1 to 3 percent o1 the acid with respect to thecaoutchouc content of. the mixture and stirring sutficiently to causethe mass to attain such consistency as to enable the mixture to bespread or stained.

In testimony whereof I aifix my signature.

RUDOLF OECKINGHAUS.

